This invention relates to an optical scanner for sensing the ratio of the "printing" to the "non-printing" area on a printing plate for automatic computer-controlled preadjustment of the ink metering elements for the printing zones in a printing machine.
Currently printing machines are operated under remote control by a central control computer accessed by a control terminal. The printing machine has several ink-dosing elements arranged across the width of the printing machine for dosing the application of ink to a printing plate, and the ink-dosing elements are individually adjustable by remote control adjusting devices. Before any sheets are fed through the printing machine, the ink dosing elements are adjusted to predetermined set points, and after several test sheets are printed, the ink densities of several control areas on the printed sheets are measured by a scanning device. A computer control compares the measured ink densities to desired ink densities in order to more precisely adjust the ink dosing elements. Such a system is described in Schramm et al. U.S. Pat. No. 4,200,932 issued Apr. 29, 1980, for which a reexamination certificate issued Apr. 26, 1983.
In order to speed up the automatic adjustment of the ink dosing elements, it is known that the ratio of the "printing" to the "non-printing" area on the printing plate, for each strip-shaped inking zone dependent on the printing press, should be determined so that the initial set points for the ink dosing elements may be determined or adjusted in accordance with that ratio. In order to determine the ratios of the "printing" to the "non-printing" area on the printing plate for the ink zones of the printing press, it is known to provide an array of photo-sensing elements along one dimension of the printing plate, which received the light of a light source reflected by the printing plate. Means are provided for relative movement of the light source and array of photo-sensing elements along the second dimension of the printing plate. As the array of photo-sensing elements scans across the printing plate, the reflected light received by each photo-sensing element is measured and recorded in a computer which is programmed to calculate the ratio of the "printing" to "non-printing" area on the printing plate for the inking zones of the printing press. Such an arrangement for scanning printing plates is described in West German Pat. No. 3,029,273.